Only half of newsletter subscribers being synced with Klaviyo

Hi! Hoping someone here can lend me some help.

Customers who subscribe to our Newsletter are being captured in two different places: in the Shopify customer’s tab, and in Klaviyo. Customers who sign up on the website are being captured in Klaviyo, while customers who opt-into the newsletter during the checkout process are captured in Shopify. I would like all newsletter subscribers to ideally be captured on both platforms, but at least capturing these emails in Klaviyo is a must.

My site is rewildorganics.org

Can anyone give me some guidance? Thank you so so much.